Hanford miniature swine are being treated with californium and radium sources using an after loading technique used in Radiotherapy for treatment of cervical cancer to expose normal tissues at risk to doses sufficiently high to cause ulceration of the rectum adjacent to the sources. Correlation is being made between the pathologic changes produced and the dose recorded on implanted dosimeters at necropsy. By this means RBE's for rectal ulceration, ureteral stricture and urinary tract injury was obtained. All were between the range of 6.2 and 6.8 for the neutron component of 252CF. The late effects of radiation treatment with neutrons are known to be of greater concern in Radiotherapy than early changes because they would result in more complications than are produced by equivalent doses of gamma radiation doses. We propose to follow the recovery from injury of these tissues where complications may occur for at least three years post-exposure to determine the RBE for 252Cf neutrons at that time. This should provide information about the effects of 252Cf on normal tissue at risk, the doses that they can tolerate, and their potential for recovery from injury by californium neutrons. BIBLIOGRAPHIC REFERENCES: Sullivan, M.F., J.L. Beamer and T.D. Mahony. Effects of Intracavitary Irradiation by Californium-252. In: Biological Effects of neutron Irradiation IAEA Symposium, 299-310, 1974.